1. Field of the Invention:
This invention relates to a testing valve insertable in a well conduit, such as a drill string, and operable by an increase in annulus pressure to shift the valve from a closed to an open position and vice versa.
2. Summary of the Prior Art:
The incorporation of a testing valve in a drill string utilized for drilling a subterranean well to effect the testing of various formations traversed by the well bore, is an expedient well known in the art. Reissue Patent 29,638 to NUTTER discloses one form of test tool heretofore utilized, involving a sleeve valve which is axially shifted between a bore opening and a bore closing position by an increase in the annulus pressure above a set packer over the hydrostatic pressure normally existing in the well annulus. The NUTTER Reissue Patent employs a nitrogen chamber to provide a reference pressure, which is substantially equal to the well annulus hydrostatic pressure. The reference pressure in the nitrogen chamber is produced by permitting well annulus fluids to enter an extension of the nitrogen chamber and impinge upon a floating piston which isolates the nitrogen gas from the well fluids. When the packer is set, and it is desired to establish a reference pressure, an isolation valve is closed, cutting off the access of the well fluids to the extension chamber below the floating piston and, thus, trapping a pressure in the compressible nitrogen gas substantially equal to the well hydrostatic pressure. Such valve is then closed by a downward manipulation of the tubing string.
Later patents, such as Patent 3,976,136 to FARLEY et al, eliminated the necessity of closing the isolation valve by tubing string manipulation through the provision of an isolation valve operable by the initial increase in pressure of the well annulus fluids over the hydrostatic pressure existing at the time the packer is set. The FARLEY et al patent also discloses the employment of a rotatable ball valve as the valve element for controlling flow of formation fluid through the tubing string in which the testing tool is mounted. The ball valve has become the most popular version of pressure-operated testing tools now available.
The operation of such ball valve involves certain specific requirements if optimum, trouble free operation is to be achieved. A tubular member is commonly employed for effecting the shifting of the ball valve from a normally closed position to an open position by downward movement of the tubular member produced by an increase in the pressure of annulus fluids. Such tubular member generally defines part of the axial passageway through the tool which communicates with the bore of the tubing string carrying the testing tool and is slidably mounted within an outer housing. Thus, the maintenance of a good sealing relationship between the top of the tubular member and the closed ball valve is a necessity. At the same time, it is highly desirable that the seal between the ball valve and the tubular operating member be broken to equalize pressure above and below the valve prior to any shifting movement of the ball valve from its normally closed to an open position. This requirement has resulted in a number of different constructions in the prior art for utilizing separate annular sealing members telescopically related to the upper end of the tubular actuating member and biased by a small spring into sealing engagement with the ball surface when the ball is in its closed position. A lost motion connection is then provided between the upper part of the tubular actuating member and the annular member which actually engages the external periphery of the ball valve, to effect its rotation from closed top open position by downward movement of the tubular actuating member.
The aforedescribed prior art arrangement, while effective, has proven to be deficient when utilizing elastomeric seals on the ball valve, and whenever a substantial fluid pressure differential exists above the closed ball valve relative to the fluid pressure existing below the ball valve. Such fluid pressure differential tends to move the annular sealing member away from the ball valve and thus destroy the elastomeric seal by fluid jet action. If the ball is rotated while the seal is engaged, the elastomeric seal is readily disintegrated.
Lastly, prior art ball valves for test tools are normally run into and pulled from the well in a closed position and must be closed at any time that pressure cannot be maintained in the annulus. This closed position limits certain desired circulating and well killing procedures. Also this closed position requires the well fluids to bypass the entire apparatus being run into the well, including the packer mounted on the tool string. This necessarily slows the introduction of the apparatus into the well by virtue of the constricted upward passage for well fluids defined between the periphery of the unset packer and the well bore.
Accordingly, it is an object of this invention to provide an annulus pressure operated test tool, and method for operating same, which will overcome the aforementioned deficiencies and/or limitations of prior art apparatus.